Phase 2 Study of Imprime PGG and Pembrolizumab in Patients With HR+/HER2- Metastatic Breast Cancer (mBCA)

The primary objective of this Phase 2 Simon 2-Stage study is to determinate the Overall Response Rate (ORR) per RECIST v1.1 following treatment with Imprime PGG + pembrolizumab in patients with ER/PR+/ HER2(-) metastatic breast cancer who have progressed through prior hormone therapy with at least one CDK4/6 inhibitor, and a maximum of 2 subsequent chemotherapy treatment. Patients will be screened for baseline anti-β glucan antibody level (ABA; measured in peripheral blood). Those patients with an ABA greater than or equal to 20 mcg/ml and meeting all other I/E criteria, will be enrolled. The study will enroll 47 patients with 23 patients enrolled into Stage 1. If 4 or more patients in Stage 1 have an objective response after 12 weeks of treatment, the study will proceed into Stage 2. A total of 24 patients will be enrolled in Stage 2 for a total combined population of 47. Overall, objective responses must be observed in 10 patients for the study to be declared a success.